1. Field of the Invention
The present invention relates to an aromatic imide-based dispersant for carbon nanotubes and a carbon nanotube composition comprising the same. More particularly, the present invention relates to an aromatic imide-based dispersant having a heterocyclic ring which is readily adsorbed on the surface of carbon nanotubes to prevent the aggregation of the carbon nanotubes and thus improve the dispersibility of the carbon nanotubes, and a nanotube composition comprising the same.
2. Description of the Related Art
Since their discovery by Dr. Sumio Iijima in 1991, carbon nanotubes (“CNT”), which are materials having a nanometer-scale size (“nano-size”) have been much studied. A CNT is a honeycomb lattice of carbon atoms rolled into a cylinder, in which one carbon atom is connected with others in a hexagonal pattern. The hexagonal patterns may be interspersed with pentagonal shapes which can impart a chiral pattern to the hexagonal lattice. Having a diameter on the order of a few nanometers, a CNT exhibits characteristic electrochemical properties.
It is known that the electrical properties of CNT are determined as a function of structure and diameter (Phys. Rev. B46, 1804 (1992); Phys. Rev. Lett. 68, 1579 (1992)). Depending on the structure of a CNT and its diameter, it can behave either as an insulator, a semiconductor or a metal. For example, when the motion of free electrons is changed in CNT by modifying the spin or chirality of the CNT, the free electrons either freely move therein, thereby transforming the CNT into a conductor, or encounter a barrier to flow, thereby transforming the CNT into a semiconductor.
Thanks to superiority in mechanical strength and chemical stability, changeability between semiconductive and conductive properties, and structural characteristics of narrow, long, and hollow tubes, CNTs are highly useful when applied to nano-size electronic elements, including flat display devices, transistors, and the like, as well as to energy storage devices.
When used to form electroconductive films or in the fabrication of various electronic devices, CNTs need to be effectively dispersed in matrices such as solutions or binders. However, CNTs show great tendency to aggregate into bundles in a matrix owing to Van der Waals force, and thus the solubility of the nanotubes in water or other solvents decreases, resulting in processing difficulty.
When aggregated in a matrix rather than dispersed, carbon nanotubes cannot exhibit characteristic useful properties and/or cannot be formed into a film which has uniform properties throughout.
This strong tendency toward aggregation makes it difficult to adequately disperse CNTs in a matrix with conventional commercially available dispersants. Extensive attempts have been made to develop novel dispersants or methods for uniformly dispersing CNTs in solvents or binders.
For instance, Korean Patent Laid-Open Publication No. 2001-102598 discloses a method of introducing an alkyl group into a CNT by a chemical linkage. An alkyl group having 8 or more carbon atoms can increase the solubility of CNTs in organic solvents to hundreds of ppm by weight, but also increases the insulative properties, thereby decreasing electroconductivity. One the other hand, a smaller alkyl group cannot adequately increase the solubility of the CNT to the desired extent while maintaining electroconductivity.
Korean Patent Laid-Open Publication No 2003-86442 discloses a method of wrapping CNTs with a polymer which is physically interactive with the nanotubes, thereby increasing the solubility thereof. However, the CNTs wrapped with the polymer are disconnected with each other so that the electroconductivity decreases. Further, in the absence of a perfect coating, the polymers as well as the carbon nanotubes can aggregate, leading to a decrease in the efficiency of the dispersant.
In Korean Patent Laid-Open Publication No. 2005-97711, a functional group selected from among cyanate, amine, hydroxy, carboxyl, halide, nitrate, thiocyanate, thiosulfate, vinyl, and combinations thereof is attached to CNTs. This method, however, injures the surface of carbon nanotubes and thereby degrades the electrical properties thereof.
Japanese Patent Laid-Open Publication No. 11-286489 discloses a pherylene compound which has improved coloristic and rheological properties, and a pigment preparation. U.S. Pat. No. 5,264,034 also discloses a pigment preparation based on a pherylene compound. However, neither coloristic pherylene pigment, addresses improved dispersibility of CNTs.